The setup described in the link you provided is to setup a stand-alone PXE server within a self-contained switch. If you have managed switches, you can VLAN this out.
Check out this site:
http://www.petenetlive.com/Tech/Windows/WDSGHOST/WDSandGHOST.htmThis will setup PXE on a windows box and uses your pre-existing DHCP.
Hope this helps